Field
The present invention relates to a micromechanical device for detecting angular velocity and especially to a micromechanical device including four detection masses for detecting angular velocity about a single rotation axis aligned with the plane of the micromechanical device. The present invention further relates to a method for operating a micromechanical device for detecting angular velocity and more particularly to a method for operating a micromechanical device including four open drive frames and four detection masses for detecting angular velocity about a single rotation axis aligned with the plane of the micromechanical device.
Description of Related Art
Micro-Electro-Mechanical Systems, or MEMS can be defined as miniaturized mechanical and electro-mechanical systems where at least some elements have a mechanical functionality. Since MEMS devices are created with the same or similar tools used to create integrated circuits, micromachines and microelectronics can be fabricated on the same piece of silicon.
MEMS structures can be applied to quickly and accurately detect very small changes in physical properties. For example, a microelectronic gyroscope can be applied to quickly and accurately detect very small angular displacements.
Motion has six degrees of freedom: translations in three orthogonal directions and rotation around three orthogonal axes. The latter can be measured by an angular rate sensor, also known as gyroscope. In MEMS gyroscopes, the Coriolis Effect is used to measure angular rate. When a mass is moving in one direction called the primary motion and rotational angular velocity is applied, the mass experiences a force in orthogonal direction as a result of the Coriolis force. Resulting physical displacement caused by the Coriolis force may be then read from, for example, a capacitive, piezoelectrical or piezoresistive sensing structure. The displacement due to the Coriolis Effect may also be called sense mode. The primary motion may alternatively be called driving motion, primary mode or drive mode.
A gyroscope is a device for detection of angular velocity. In MEMS gyroscope, mechanical oscillation is used as the primary motion. When an oscillating gyroscope is subjected to an angular motion orthogonal to the direction of the primary motion, an undulating Coriolis force results. This creates a secondary oscillation, also referred to as the sense mode or the detection motion, orthogonal to the primary motion and to the axis of the angular motion, and at the frequency of the primary oscillation. The amplitude of this coupled oscillation can be used as the measure of the angular rate, which term may refer to the absolute value of an angular velocity.
U.S. Pat. No. 7,421,897 presents an inertial sensor with a cross-quad configuration of four resonator elements. Frames of the adjacent resonator elements are coupled to each other in order to force the frames into anti-phase movement. Resonators are suspended within the frames.
U.S. Pat. No. 8,261,614 presents a rotational speed sensor including two capacitively driven resonator elements with a coupling bar placed between two seismic masses for supressing translatory deflections of the seismic masses in reading mode.